This invention relates in general to wood beams and more particularly to wood I-beams and a method of fabricating such beams.
The typical wood I-beam of the type used in the construction of buildings consists of three all wood components--namely, a pair of flange pieces that are spaced apart and parallel and a web that extends between and along its opposite edges is joined to the flange pieces. Usually each flange piece is 2".times.3" or 2".times.4" nominal dimension lumber, while the web is 3/8" or 1/2" plywood. The resulting beam possesses substantial strength, yet is light in weight and easily handled. Moreover, flooring or other beams may be secured to it with simple nails.
Normally, the web is glued along its edges to the flange pieces, so the strength of the beam to a large measure depends on the strength of the glue joints that hold its components together. These glue joints usually lie within grooves that are cut into the flange pieces and receive the opposite edges of the web. To effect a good glue joint, pressure must be exerted between the side walls of the groove and the abutting web surfaces while the glue sets.
One procedure for developing adequate pressure at the glue joint forms the subject matter of U.S. Pat. No. 3,490,188. In this procedure the side edges of the web are passed between dies which compress the plywood at its edges and impart slight bevels to those edges. The grooves are milled into the flange with their side walls beveled at a corresponding angle. Thus, by reason of the wedge shape, a tight fit exists between the beveled edges of the webs and the tapered surfaces of the grooves in which those edges are received. This provides the force necessary to enable the glue to set up and create a strong bond.
In another procedure, which forms the subject matter of U.S. Pat. No. 4,195,462, each flange piece contains a pair of closely spaced grooves which diverge somewhat from the surface out of which they open. The web, on the other hand, has a relatively wide slot cut into its opposite edges, so that each edge possesses a pair of legs that extend the full length of the web, each rib being about as wide as a groove in the flange piece. Initially, the legs along each end edge are parallel, but when the legs are forced into the grooves in the flange pieces they flare outwardly and assume the divergence of the grooves. This distortion of the legs forces the inside faces of the legs against the inside walls of the grooves and thereby provides the pressure that is necessary to effect a strong bond at the glue joint.